ES2304584T3 - SEALING DEVICE TO PRODUCE SEALED CONTAINERS OF A VERTIBLE FOOD PRODUCT. - Google Patents

Abstract

The sealing device (1) has a supporting frame (6); at least a first and a second jaw (12,13) opposite each other and movable cyclically with respect to the frame (6) and along part of the path (A); sealing means (29) carried by the first jaw (12) to seal the tube (3); and electromagnetic power means (50) for supplying electric energy to the sealing means (29); the power means (50) having at least one primary winding (56) fixed to the frame (6) laterally with respect to the path (A) and connectable to an electric energy source, and a secondary winding (63) carried by the first jaw (12), powering the sealing means (29), and receiving electric energy by electromagnetic induction from the primary winding (56) as the first jaw (12) travels past the primary winding (56).

Description

Sealing device to produce containers sealed from a pourable food product.

The present invention relates to a sealing device to produce sealed containers of a product of pourable feed.

As it is known, many food products poubles, such as fruit juice, pasteurized milk or UHT (treated at ultra-high temperature), wine, sauce of tomato, etc. they are sold in containers made of material sterilized packing.

A typical example of this type of packaging is the parallelepiped shaped container for food products liquid or spillable known as Tetra Brik Aseptic (brand registered), which is made by folding and sealing the material of laminated strip packaging.

The packaging material usually has a multilayer structure comprising a layer of material fibrous, for example, paper, covered on both sides with layers of heat sealing plastic material, for example, polyethylene.

In the case of aseptic containers for products Long-term storage, such as UHT milk, the packaging material comprises a layer of material barrier, for example, an aluminum foil or EVOH, which is superimposed on a layer of plastic sealing material by heat, and is in turn covered with another layer of plastic material heat sealed that eventually forms the inner face of the container containing the food product.

As is known, packages of this type are produced from fully automatic packaging machines, in which forms a continuous tube from the material of continuous sheet packaging. More specifically, the sheet Continuous packing material unwinds from a reel and is supplied through an aseptic chamber on the packing machine, in which it is sterilized, for example applying a sterilizing agent such as peroxide hydrogen, which is subsequently evaporated by heating, and / or subjecting the packaging material to intensity radiation and appropriate wavelength; and the sterilized continuous sheet is kept in a sterile, closed environment and bends in a cylinder and it is sealed longitudinally to form a continuous tube so known.

The tube of packing material, which in effect forms an extension of the aseptic chamber, is supplied in a vertical direction, it is filled with the food product sterile or sterile processed, and is supplied to through a sealing device to form the containers individual. That is, inside the sealing device, the tube it is sealed in a number of cross sections equally separated to form a continuous strip of pillow containers connected to each other by respective sealing bands transversal, that is to say that it extends perpendicularly in the direction of travel of the tube. Pillow containers are separated by cutting the relative transverse sealing bands, and they are transported to a bending station where they are folded mechanically to form respective containers with final shape of parallelepipeds

Packaging machines are known as has been described, for example in the European patent EP-B-0887265, comprising two chain conveyors that define respective paths without end and fixed with a respective number of sealing jaws. The two paths have respective ramifications that are face substantially and are parallel to each other, and between which tube of packaging material is supplied so that the jaws of a transporter cooperate with the corresponding jaws of the other conveyor along said ramifications of the respective paths, for grabs the tube in a number of successive cross sections, and for Seal and cut the containers.

Packaging machines are also known. which comprise only two pairs of jaws, which act alternatively on the tube of the packing material for grab and seal, for example, heat sealing, along a certain number of cross sections equally separated.

When the sealing operation is completed, a cutter, carrier, for example, by one of the jaws of each pair and that interacts with the tube of material used, is activated to cut it along the center line of the cross section that has just been sealed, and thus separate a pillow pack from the lower end of the tube of packing material. The lower end that is transversely sealed, the relative jaws, which reach the lower dead center position, can be opened to avoid interference with the upper part of the tube. At the same time, the other pair of jaws, operated in exactly the same way, move down from the upper dead center position, and repeat the previous process of gripping / forming, sealing and
cut.

In both types of packaging machine, the part of the tube caught between each pair of jaws is typically sealed by means of carrier heating by one of the jaws, and that melt the layers of plastic material locally Heat seal grabbed between jaws.

In the case of aseptic containers with a layer of electrically conductive material, typically aluminum, such as Barrier material, the tube cross sections are normally sealed by introducing a current of electrical loss in the aluminum layer, so that it melts locally heat sealing plastic material.

More specifically, one of the jaws of each pair comprises a main body of non-conductive material, and a inductor housed in a front seal of the main body; and the another jaw has flexible material pressure pillows, for example rubber.

The inductor is activated when the relative torque of jaws grab the tube to seal a cross section of the tube sealing with heat in plastic cover material.

In the case of packaging without an aluminum layer or other electrically conductive material, for example packages with a EVOH barrier layer, the tube cross sections are normally sealed using a hot rod to heat locally packing material inwards.

More specifically, one of the jaws is fixed with the hot rod, while the other is normally fixed with one or more flexible material pressure pillows. He called "hot rod" sealing method described requires a relatively prolonged contact between the hot rod and the packing material.

To accelerate the localized fusion of the material packing, and thus increase the production speed of  packaging, sealing devices are widely used ultrasound These substantially comprise a generator of mechanical vibration, or sonotrode, and an anvil, for example, as described in document 615907, which are fixed at respective jaws of each pair, and cooperate with each other to heat the packing material by vibration of ultrasound

In all previous solutions, the media heating or sealing that can be moved with the jaws relative must be electrically activated by force of fixed electrical energy at a predetermined point along the tube path of the packing material. In others words, electrical energy must be transferred from a fixed source to a mobile user device along a part of the user device path.

This can be done using substantially two methods, each of which, however, has disadvantages and limitations.

In a first method, the jaws fixed with the heating means are also fixed with brushes preferably made of carbon, and that, along a predetermined part of your tour, slide along bars of copper power fixed to the machine frame packing

The rapid wear of brushes and contact not stable between brushes and power bars are the main disadvantages of this method, which also tends to worsen when the machine's output rate packaging increases.

To eliminate these disadvantages, few years, a method has been perfected by which energy electric is transferred from the fixed source to the device mobile user by electromagnetic induction. An example of This method applied to chain type packing machines is described in Patent Application WO 00/64662, and an example similar, applied to a packaging machine that characterized because it only has one pair of jaws, described in EP-B-0732190.

In both cases, the electrical energy is transferred from a transmission unit, fixed to the frame of the packaging machine, to a receiving unit fixed to one of the jaws in a relative pair.

The transmission unit has a core Fixed magnetic with a primary winding connected to the source of electric power, and the receiving unit has a core Integral mobile magnetic with relative jaw body and fixed with a secondary winding connected to the means of heating. When the receiving unit moves past the transmission unit, the electric current is induced in the secondary winding to activate the heating means.

Without contact between the units of reception and transmission, the above method solves the problem of wear.

On the one hand, the transfer systems of electric power by induction described in the documents Above are ineffective and highly sensitive to vibrations in air separation between the cores of the transmission unit and reception. Since the side of the air gap depends on the inevitable connection tolerances of the component parts of the packaging machine, the solutions described in the previous documents fail to ensure, today, the necessary reliability of the energy transfer system employee.

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Patent application WO 00/64662, in In particular, it uses an opposite E configuration for the cores Fixed and mobile. More especially, each core comprises a part of bar, from which three perpendicularly extend parallel branches and, in use the branches corresponding face of the other core.

The tests carried out by the Applicant in this type of core configuration of the transmission units and reception show a considerable increase in the dispersion of magnetic flux and in the magnetization current next to small increases in air separation between fixed cores and mobile.

In Figures 7 and 8, the curves W_ {3} and M_ {3} show, for an opposite E configuration of the cores  fixed and mobile, apparent power and magnetization current along with an increase in air separation between the cores. As you can see, the curves are characterized by relatively high values of magnetization current and the apparent power, and changes steeply, confirming thus the extreme sensitivity of the WO document solution 00/64662 to variations in air separation between Fixed and mobile cores.

It is an object of the present invention provide a sealing device to produce containers sealed from a pourable feed product, designed to eliminate, in a simple way and with low cost, the disadvantages above mentioned typically associated with devices known sealing, and which, in particular, employs a system of efficient electromagnetic electrical energy transfer insensitive to air separation between the transmission part Fixed and mobile reception part.

In accordance with the present invention, provides a sealing device to produce sealed containers  of a pourable feed product, as claimed in the Claim 1.

A preferred, non-limiting embodiment of the The present invention will be described by way of example with reference to the attached drawings, in which:

Fig. 1 shows a perspective view, with part removed for clarity, from a sealing device in accordance with the teachings of the present invention;

Fig. 2 shows a schematic side view of the sealing device of Figure 1;

Figure 3 shows a larger scale view in Perspective of part of the sealing device of Figure 1:

Figure 4 shows a larger scale view in perspective of a detail of Figure 3;

Figure 5 shows a section on a larger scale than along the V-V line of Figure 4;

Figure 6 shows the same section as in the Figure 5, of a variation of the detail of Figure 4;

Figures 7 and 8 show comparative graphs of the characteristic quantities of the sealing devices of in accordance with the teachings of the present invention; and the known sealing devices.

The number 1 of Figures 1 and 2 indicates as a a whole sealing device to produce continuously sealed containers 2 of a pourable food product, such as pasteurized milk or UHT, fruit juice, wine, etc., from a tube 3 of packing material.

The tube 3 is formed in a known way, waters above device 1, bending longitudinally and sealing a Continuous sheet of heat sealing sheet material, and it is filled with sterile or sterile processed food product for packing.

The device 1 comprises a frame 6 (Figures 1 and 3) defined by two side walls 7a, 7b and by two parallel transverse walls 8a, 8b rigidly fixed between the side walls 7a, 7b to define, with the walls lateral 7a, 7b, a cavity 9; and two chain conveyors 10, 11 supported by the frame and having respective jaws 12, 13 (only a couple of which is shown in Figure 1) that cooperate with each other to interact with tube 3 of material packaging supplied along a path vertical A, through the cavity 9.

With particular reference to Figure 2, the conveyors 10, 11 define respective endless paths P, Q, along which the jaws 12, 13 are supplied, and that extends around the respective walls 8a, 8b of the frame 6.

The conveyor 10 comprises a chain articulated 15 extending along the path P; and two drive wheels 16 that engage with both sides of the chain 15 at the lower end of the path P. The jaws 12 they are an integral part, and define alternating joints of the chain 15, and are connected to each other in an articulated manner by pairs of bars 17.

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More specifically, each jaw 12 (Figures 1-3) comprises a main body 20, which is elongated in a direction B perpendicular to path A and a the side walls 7a, 7b, and have respective elongations ends 21, 22, want each of which a first and second pins 23, 24 that have separate C, D axes and parallel to the direction B. The bars 17 pivot on the pins 23, 24 of the jaws 12 for connecting the pins 23 of the jaw 12 to the pins 24 of the adjacent jaw 12.

In the same way, the conveyor 11 (Figures 1 and 2) comprises an articulated chain 25 extending to path length Q; and two drive wheels 26 which mesh with chain 25 at the lower end of the path Q. Chain 25 is defined by a certain number of jaws 13 connected to each other in an articulated way, and only described with detail to the extent that they are different from the jaws 12, and require for the clarity of understanding of the present invention. The parts of the jaws 13 identical or corresponding to part of the jaws 12 described are indicated using the Same reference numbers. Briefly, each jaw 13 comprises a main body 20 that has pairs of pins ends 23, 24 on which the connecting rods 17 pivot with adjacent pairs of the jaws 13.

Each jaw 12 (figures 1 to 3) comprises a heating member 29 fixed to a main body 20, parallel to address B, as defined, in the example shown, by an electrically activated inductor as has described in detail below.

Alternatively, each jaw 12 can accommodate a different type of heating member, for example, a electrically operated sonotrode for sealing ultrasound.

Instead of heating member 29, each jaw 13 comprises a pressure bar 32, which cooperates with the heating member 29 of the corresponding jaw 12 for grab a cross section of tube 3 (Figure 2), and it has, at the front, one or more bands of elastomeric material flexible.

The jaws 12 and 13 (figures 1 and 3) they also comprise respective devices 33 for controlling the container volume 2 when the containers are sealed. Each device 33 that is known, for example from the document EP-B-0887265, and therefore not describes in detail, substantially comprises a half wrapped 34 articulated to a main body 20, around an axis parallel to the C, D axes by means of two integral support brackets with half wrapped 34.

As shown in Figure 1, each average wrapped 34 cooperates in the front with the half wrapped complementary 34 to form a substantially shaped cavity parallelepipedic to accommodate a package 2 that is being formed. Each device 33 also comprises a cam follower roller 36 fixed to a support bracket in turn fixed integrally to the back of the relative half wrapped 34.

Each of the follower rollers 36 of the jaws 12 and 13 cooperate with the respective cams 38 fixed to the walls 8a and 8b of the frame 6, and of which only the associated with the conveyor 11 it can be seen in Figure 1.

The movement of the jaws 12 and 13 is controlled by the respective cam pairs 40, 41 fixed to the walls 8a, 8b of the frame 6 and cooperating with the respective pairs of cam follower rollers 42, 43 fixed to the extreme elongations 21, 22 of the jaws 12 and 13. The Rollers 42, 43 of each pair are coaxial with pins 24, 23, respectively, and are axially offset one with respect to another to cooperate with the respective cam 40, 41.

More specifically, wall 8a (figures 1 and 2) it is fixed with two pairs of cams 40, 41 that cooperate with respective pairs of rollers 42, 43 of the jaws 12; and of similarly, wall 8b is fixed with two pairs of cams 40, 41 cooperating with respective pairs of rollers 42, 43 on the jaws 13.

The cams 40, 41 have respective parts substantially U-shaped 40a, 41a that extend around of the upper edges of the respective walls 8a, 8b, for define return parts, opposite to respective wheels of drive 16 and 26 for the respective chains 15, 25 of the conveyors 10, 11; respective parts 40b, 41b that are they extend along respective walls 8a, 8b, within the cavity 9. Parts 40a, 41a define parts P_ {1}, Q_ {1} of the two paths P, Q, along with jaws 12 and 13 are they move towards each other and impact the tube 3 of material packing; and parts 40b, 41b define parts of confrontation, substantially parallel P2, Q2 of the two parts P, Q, along which the jaws 12 and 13 are kept in contact under pressure to form the packages sealing joint 2 in the respective sealing bands 443 transversal, substantially flat. A continuous strip is like this formed, comprising a number of shaped container parts parallelepipedic 45 connected to each other by sealing bands 44 that are cut either along the path P or waters below the device 1 to form the containers 2.

Cams 40, 41 release the relative chains 15, 25 in the respective parts P 3, Q 3 of the trajectories P, Q at the exit of the respective wheels of drive 16, 26.

Along the parts P 3, Q 3, the chains 15, 25 cooperate with the respective tension pairs 46 to keep chains 15, 25 tight enough to ensure contact between the rollers 42, 43 of the jaws 12, 13 and the relative cams 40, 41.

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With particular reference to figures 3, 4, 5, device 1 also comprises a power set electromagnetic 50 to supply electric power to the member of heating 29 of each jaw 12 along the part P_ {2} of the path P.

The power set 50 comprises substantially transmission means 51 connected to a source of fixed electric power (not shown) and fully fixed to frame 6; and receiving means 52 fixed to the jaws 12 and that receive electrical energy by electromagnetic induction coming from the transmission means 51 when the jaws are they move past the transmission means 51.

More specifically, the transmission means 51 they comprise two confrontation transmission units 53, separated, fixed to the respective walls 7a, 7b, within the cavity 9, and which extend symmetrically on opposite sides of the path A and the part P_ {2} of the path P of the jaws 12.

More specifically, each transmission unit 53 is elongated in a direction parallel to path A and the part P2 of the path P, and substantially comprises a support bracket 54 of plastic material, a magnetic core fixed 55, and a primary winding preferably of copper 56 connected to the power source.

The fixed core 55 is defined by a plate elongated rectangular in the direction of path A, fixed to the bracket 54, and protruding into the cavity 9 from the bracket 54.

The fixed core 55 is made of material electromagnetic and comprises a base part shaped parallelepiped 58, from which a certain number of, in the example shown, four, parallel projections 58 protrude in the direction B towards the jaws 12 (figure 5).

The primary winding 56 comprises two plates elongated conductors 59 fixed to, and protruding from, the respective central projections 58 of the fixed core 55, so that they form extensions of protrusions 58 into the cavity 9.

The receiving means 52 comprise two series of receiving units 60 set alternately to the elongations 21, 22 of the respective jaws 12 and that interact with the respective transmission units 53.

Each receiving unit 60 (figures 3 and 4) protrudes from a relative elongation 21, 22 of the jaw relative 12, and substantially comprises a support bracket 61, a mobile magnetic core 62, and a secondary copper winding 63, that receives electrical energy by electromagnetic induction from the primary winding 56 when the receiving unit 60 is shifts past the relative transmission unit 53.

In the example shown, the mobile core 62 is defined by a body preferably made of ferrite, which protrudes from the relative elongation 21, 22 of the relative jaw 12 towards the relative wall 7a, 7b of the frame 6, and having a preferably E-shaped section in a plane perpendicular to the trajectory A.

More specifically, the mobile core 62 comprises a base part 64 in the form of a rectangular plate, from the which three parallel projections 65 protrude in the direction B towards the relative side wall 7a, 7b (figure 5).

In the example shown, the secondary winding 63 comprises a plate conduit 66 having an end portion 67 rolled to form a turn around the central projection 65 of the mobile core 62; and an elongated part 68 that connects the end portion 67 to the heating member 29.

According to an important aspect of the present invention, when the transmission and reception means 51, 52 are interconnected by electromagnetic induction, it is say, along the part P_ {2} of the path P, each receiving unit 60 and relative transmission unit 53 are arranged so that the conductive plates 59 of the winding primary 56 and the end portion 67 of the secondary winding 63 is entwine in the direction B. In other words, along the part P2 of the path P, the conductive plates 59 of each primary winding 56 face the opposite sides of the end portion 67 of the relative secondary winding 63 in a direction E perpendicular to path A, direction B, and therefore to the walls 8a, 8b of the frame 6.

When transmitting and receiving members 51, 52 are interconnected by electromagnetic induction,  the fixed and mobile cores 55, 62 of each transmission unit 53 and the relative receiving unit 60 preferably also entwine in direction B, that is, the protrusions 58, 65 of one of the cores 55, 62 are housed within the respective cavities limited by the projections 65, 58 of the other core 62, 55.

The member 53 'of Figure 6 indicates as a a whole variation of the transmission unit according to the teachings of the present invention and described below only to the extent that it differs from the transmission unit 53. Any parts of the corresponding transmission unit 53 ' or equivalent to those of the transmission unit 52 already described are indicated, when possible, using the same numbers of reference.

The transmission unit 53 'differs substantially of the transmission unit 53 comprising a 55 'fixed magnetic core with rectangular plate shape without projections, and from which two conductive plates protrude 59 ' identical to the conductive plates 59.

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In this case, when the transmission members and reception 51, 52 are interconnected by induction Electromagnetic, primary winding 56 and secondary winding 62 interlock in direction B (i.e. plates conductors 59 'of one of the primary windings faces the assumed sides of the end portion 67 of the secondary winding relative 63 in the direction E), but the fixed core 55 'and the core mobile 62 no.

Figures 7 and 8 show two graphs of comparative tests of the characteristic amounts of sealing devices 1 that use the configurations of the Figures 5 and 6 of the fixed core 55, 55 'and the mobile core 52, and a sealing device that uses the opposite E configuration known of fixed and mobile cores, as described in the Patent Application WO 00/64662, respectively.

More specifically, the graph in figure 7 shows the magnetization current M as a function of the air separation G between the fixed and mobile cores of the different sealing devices As you can see, the current of magnetization remains much lower for sealing devices 1 according to the invention (curves N1 and M2 for configurations of figures 5 and 6, respectively) which for the known sealing devices that employ an E configuration opposite of the fixed and mobile nuclei (curve M_ {3}).

In addition, as the air separation G increases, the magnetization current M remains more or less constant (M_ {1}) for the configuration of Figure 5 of the sealing device 1, increases slightly (M2) for the configuration of figure 6 of the sealing device 1, and increases clearly (M_ {3}) for the sealing device that employs a opposite E configuration of fixed and mobile cores.

Similarly, the graph in Figure 8 shows the apparent presentation W_ {A} based on the separation of G air between the fixed and mobile cores of the various devices sealing. As can be seen, the apparent power W_ {A} remains much lower for sealing devices according with the invention (curves W_ {1} and W_ {2} for configurations of figures 5 and 6 respectively) which for devices of sealed using an opposite E configuration of the cores fixed and mobile (curve W_ {3}).

In addition, as the air separation G increases, the apparent power W_ {A} remains more or less constant (W_ {1}) for the configuration of Figure 5 of the sealing device 1, increases slightly (W2) for the configuration of figure 6 of the sealing device 1, and increases clearly (W_ {3}) for the known sealing device that employs an opposite E configuration of the fixed cores and mobile.

Briefly, the graphs of figures 7 and 8 show the configuration of figure 5 of the sealing device 1 characterized by apparent power values W_ {A} lower, which are more effective in energy transfer electrical, and that are less sensitive to variations in the size of the air separation between the fixed core 55 and the mobile core 62. Although still sensitive to variations in the size of the air separation between the fixed core 55 'and the mobile core 62, the configuration of figure 6 is even more superior, in terms of transfer of electric power and apparent power W_ {A} low, to the known solution that employs an opposite E configuration of Fixed and mobile cores.

The sealing device works as follow.

The two conveyors 10, 11 are rotated in opposite directions, as indicated by the arrows on the Figure 2, so that the respective jaws 12 and 13 cooperate with tube 3 of the packing material from the end of the respective parts P_ {1}, Q_ {1} of the paths P, Q and along the respective parts P_ {2}, Q_ {2} with a law of movement determined by cam profiles 40, 41.

The operating cycle will be described at continued in more detail with reference to a jaw 12 of the conveyor 10 and the corresponding jaw 13 of the conveyor eleven; all jaws 12 and 13 obviously perform the same cycle in time intervals that depend on the departure rate.

Along the parts P_ {1} and Q_ {1}, the jaws 12 and 13 are carried together to gradually deform and eventually "flatten" tube 3 in a transverse band 44.

At the end of the parts P_ {1}, Q_ {1}, the devices 33 to control the volume of packets 2 are activated; and the wrapped stockings 34 of the jaws 12 and 13 are carried together frontally to define a cavity shaped parallelepiped that defines the volume of container part 45 of the container 2 that is being formed.

Along the respective parts P2, Q_ {2} of trajectories P, Q, jaws 12 and 13 are held firmly against tube 3; at whose stage, the unit of reception 60 of the jaw 12 travels past the unit of relative transmission 53 and is coupled in the B direction.

More specifically, depending on the design of the fixed core (55 or 55 ') the receiving unit 60 is placed with with respect to the relative transmission unit 53, in one of the configurations shown in figures 5 and 6. In both cases, when the jaw 12 travels along the part P2 of the path P, the electric current is induced by the primary winding 56 in the secondary winding 63 of the unit relative reception 60 to the power heating member electric 29, which seals the two overlapping parts of the material of packaging forming the band 44.

When the receiving unit 60 is decoupled from the relative transmission unit 53 at the end of the part P_ {2} of the path P, the electric current ceases to be induced in secondary winding 63; is whose point, the jaws 12 and 13 release the newly formed sealing band 44 and remove the packaging strip 2.

Clearly, changes can be made in the sealing device 1 as described herein, without however they leave the field of the invention as defined in the attached claims.

In particular, device 1 may have the characteristic of one or more pairs of jaws 12, 13 that act cyclically on the tube 3 of packing material.

In addition, the design of the fixed and mobile cores 55, 55 ', 62 can be reversed, and one of them can even understand only two projections, that is, have a C-shaped section in a plane perpendicular to path A.

Claims (7)

1. A sealing device (1) to produce sealed containers (2) from a tube (3) of a sheet of packing material supplied along a feeding path (A) and continuously filling with a pourable power product, said device comprising sealing (1): - a support frame (6); - at least one pair of opposite jaws (12, 13) that can be cyclically moved with respect to said frame (6) and along part of said path (A) to grab firmly said tube (3) of packing material in regularly separated cross sections; - sealing means (29) carried by a first (12) of said jaws (12, 13) to seal said tube (3) of packing material in said sections transversal; Y - electromagnetic power means (50) for supplying electrical energy to said sealing means (29), said power means (50) comprising at least one winding primary (56) fixed to said frame (6) laterally with respect to said path (A) and that can be connected to a source of electric power, and a secondary winding (62) carried by said first jaw (12), which activates said sealing means (29), and that receives electrical energy by electromagnetic induction from said primary winding (56) as said first jaw (12) moves past the primary winding (56). characterized in that, when interconnected by electromagnetic induction, said primary winding and said secondary winding (56, 63) are arranged so that they have respective adjacent parts (59, 67) that are interwoven in a first direction (B) transversely to said path (A), and because said adjacent parts (59, 67) of said primary winding and said secondary winding (56, 63) face each other in a second direction (E), perpendicular to said first direction (B) and to said path (A), when the primary winding and the secondary winding (56, 63) are interconnected by induction. 2. A device according to claim 1, characterized in that said primary winding and said secondary winding (56, 63) are respectively carried by a fixed magnetic core (55, 55 ') integral with said frame (6) and by a core mobile magnetic (62) integral with said first jaw (12); having at least one (62) of said cores (55, 55 '; 62) at least two projections (65) projecting in said first direction (B) towards the other of said core (55, 55') when said primary winding and said secondary winding (56, 63) are interconnected by induction. 3. A device according to claim 2, characterized in that said at least one (62) of said cores (55, 55 '; 62) has an E-shaped section in a plane perpendicular to said path (A). A device according to claim 2 or 3, characterized in that the other of said cores (55 ') is in the form of a plate, and that one (67) of said adjacent parts (59, 67) of said primary winding and said secondary winding (56, 63) is carried by one of said projections (65) of said at least one (62) of said cores (55 '; 62), while the other said adjacent part (59) protrudes from the other said core (55 '). A device according to claim 2 or 3, characterized in that, when interconnected by electromagnetic induction, said first core and said mobile core (55, 62) are interwoven in said first direction (B). A device according to claim 5, characterized in that said fixed core and said mobile core (55, 62) both have protrusions (58, 65); and because, when interconnected by electromagnetic induction, said projections (65) of one of said cores (62, 55) are housed within respective separations limited by the projections (58) of the other core (55, 62). A device according to any one of the preceding claims, characterized by comprising a first device (10) having a number of first jaws (12) and defining a first endless path (P) along which said first jaws (12) move; and a second conveyor (11) having a number of second jaws (13) and defining a second endless path (Q) along which said second jaws (13) move; said first and second path (P, Q) comprising respective working parts (P1, P2; Q_ {1}, Q2}) adjacent to said path (A) of the tube (3) of the material of packing and extending substantially symmetrically on opposite sides of said path (A), such that said first jaws (12) cooperate with the respective second jaws (13) to firmly grip and seal said tube (3) in respective cross sections.